1. Field of the Invention
The present invention relates to a node to relay the Ethernet frame and a frame transfer method.
2. Description of the Related Art
Conventionally, a node in Ethernet is controlled with a network control frame shown in FIG. 18 storing the network control information 12006 in the payload section and the address of the node to be controlled in the MAC address (Destination MAC address 2001 and the source MAC address 2002) and the IP address (IP address of controlled terminal 12004).
Therefore, while the user uses the entire network bandwidth for data transmission, the node cannot send the control frame. In addition, the control frame needs to have at least 64 bytes regardless of the control information amount for the node according to Ethernet standard specified by IEEE802.3.
IEEE802.1Q, that provides for the technology related to the VLAN, specifies that a VLAN tag shall be given to a frame during frame relay for network separation.
Therefore, the node that relays conventional Ethernet frames has a function to process at most one VLAN tag at a time in frame relay and the forwarding table to store the VLAN tag information given during such frame relay assures an information area for one VLAN tag only.
In addition, since the VLAN tag in the frame is the information for network separation, the node that relays the frame with VLAN tag does not have a function to change the contents of the VLAN tag. The information in the VLAN tag is used for frame transfer only.
Further, in transmission of the VLAN frame at the data link layer, the frame is relayed and the transfer port is determined by reference to the MAC address and the VLAN ID.
The conventional node control in Ethernet as described above has drawbacks as follows:
Firstly, the conventional node in Ethernet as specified in IEEE802.3 is controlled using the frame storing the control information in the payload section and the address of the node to be controlled in the MAC address and the IP address as shown in FIG. 18. Thus, while the user uses the entire network bandwidth for data transmission, the node cannot send the control frame.
Secondly, the control frame needs to have at least 64 bytes regardless of the control information amount for the node according to Ethernet standard. If the control frame is frequently sent in the network, it may oppress the bandwidth of the user data.
Thirdly, when the VLAN tag is given for frame transfer, several VLAN tags cannot be provided because there is no information area in the forwarding table.
Fourthly, in case a loop network is formed in IEEE802.3 Ethernet, because a function to discard frames when a loop of packet transfer is generated in VLAN packet transfer at the data link layer has not been realized, the looped packets occupy the network or induce oppression of the packet memory in the system, which results in unstable status of the network.